In certain mechanical or structural applications it is necessary to effectively prevent the possibility of a spark being generated between two conductive fixing elements, or between a fixing element and another conductive element, which are at a different electric potential. These different electric potentials can be caused by the presence of an electric current, by electric impacts such as lightning or an atmospheric discharge, by a static charge due to friction, etc.
In some applications, preventing these discharges can be a safety requirement, such as for example in the fixings in border areas or of areas inside the fuel storage tanks of aircraft.
There are several known processes for preventing these discharges from occurring between fixing elements:                arranging the fixing elements with one another or the fixing element and the other conductive component at a distance that is suitable and sufficient to prevent discharges;        electrically connecting the fixing elements to one another or the fixing element and the other conductive component such that they reach the same electric potential;        arranging an insulating barrier between the fixing elements or between the fixing element and the other conductive component.        
The first known solution has the problem of not being able to be used in those cases in which there is an important space limitation, therefore the fixing elements or the fixing element and the other conductive component cannot be sufficiently separated.
The second solution used in the state of the art has the drawback of the need for additional components which must be specifically designed according to the necessary fixing, which involves higher costs and the need to use non-standard components.
There are known solutions for providing an insulating barrier between the fixing elements or between the fixing element and the other conductive component, such as for example arranging a protective surface seal or paint in the previous elements. This method can be effective when the paint or seal layer has dielectric properties, but said layer or paint is subject to wear and aging, therefore it loses its insulation properties.
Another known solution consists of arranging an additional dielectric component, a glass fiber angle bar for example, between two fixing elements and another conductive component. This method is effective but requires specific designs for complex applications, an additional problem arising when the distance between the elements is small and there is not enough space to arrange this additional dielectric component.
Another known solution consists of arranging a dielectric cover or cap in at least one of the fixing elements. All the known solutions using this system install the mentioned dielectric cover or cap by pressure on the fixing element, which has the drawback that the cover or cap is damaged on numerous occasions during the installation, while at the same time the mentioned cap or cover can be lost when it is subjected to vibrations, which is very common in the operation of aircraft.
The present invention is aimed at solving these drawbacks.